Small-Scale Spatial Variations of Air-Sea Heat, Moisture, and Buoyancy Fluxes in the Tropical Trade Winds

Observations from two autonomous Wave Gliders and six Lagrangian Surface Wave Instrument Float with Tracking drifters in the northwestern tropical Atlantic during the January-February 2020 NOAA Atlantic Tradewind Ocean-atmosphere Mesoscale Interaction Campaign (ATOMIC) are used to evaluate the spatial variability of bulk air-sea heat, moisture, and buoyancy fluxes. Sea surface temperature (SST) gradients up to 0.7 degrees C across 10-100 km frequently persisted for several days. SST gradients were a leading cause of systematic spatial air-sea sensible heat flux gradients, as variations over 5 Wm(-2) across under 20 km were observed. Wind speed gradients played no significant role and air temperature adjustments to SST gradients sometimes acted to reduce spatial flux gradients. Wind speed, air temperature, and air humidity caused high-frequency spatial and temporal flux variations on both sides of SST gradients. A synthesis of observations demonstrated that fluxes were usually enhanced on the warm SST side of gradients compared to the cold SST side, with variations up to 10 Wm(-2) in sensible heat and upward buoyancy fluxes and 50 Wm(-2) in latent heat flux. Persistent SST gradients and high-frequency air temperature variations each contributed up to 5 Wm(-2) variability in sensible heat flux. Latent heat flux was instead mostly driven by air humidity variability. Atmospheric gradients may result from convective structures or high-frequency turbulent fluctuations. Comparisons with 0.05 degrees-resolution daily satellite SST observations demonstrate that remote sensing observations or lower-resolution models may not capture the small-scale spatial ocean variability present in the Atlantic trade wind region.

Automated summary

The spatial variability of air-sea heat, moisture, and buoyancy fluxes in the northwestern tropical Atlantic during the January-February 2020 ATOMIC campaign was evaluated using observations from autonomous Wave Gliders and Lagrangian drifters. The study found that sea surface temperature gradients were the leading cause of systematic air-sea sensible heat flux gradients, while wind speed gradients played no significant role. The study also suggested that atmospheric gradients may result from convective structures or high-frequency turbulent fluctuations.